[C++][Modules] A module directive may only appear as the first preprocessing tokens in a file (#144233)

This PR is 2nd part of
[P1857R3](https://github.com/llvm/llvm-project/pull/107168)
implementation, and mainly implement the restriction `A module directive
may only appear as the first preprocessing tokens in a file (excluding
the global module fragment.)`:
[cpp.pre](https://eel.is/c++draft/cpp.pre):
```
module-file:
    pp-global-module-fragment[opt] pp-module group[opt] pp-private-module-fragment[opt]
```

We also refine tests use `split-file` instead of conditional macro.

Signed-off-by: yronglin <yronglin777@gmail.com>

1 files changed, 46 insertions, 1 deletions

diff --git a/clang/unittests/Lex/LexerTest.cpp b/clang/unittests/Lex/LexerTest.cpp
index 381755d..33c8abb 100644
--- a/clang/unittests/Lex/LexerTest.cpp
+++ b/clang/unittests/Lex/LexerTest.cpp
@@ -49,7 +49,8 @@ protected:
   }
 
   std::unique_ptr<Preprocessor> CreatePP(StringRef Source,
-                                         TrivialModuleLoader &ModLoader) {
+                                         TrivialModuleLoader &ModLoader,
+                                         StringRef PreDefines = {}) {
     std::unique_ptr<llvm::MemoryBuffer> Buf =
         llvm::MemoryBuffer::getMemBuffer(Source);
     SourceMgr.setMainFileID(SourceMgr.createFileID(std::move(Buf)));
@@ -61,6 +62,8 @@ protected:
         PPOpts, Diags, LangOpts, SourceMgr, HeaderInfo, ModLoader,
         /*IILookup =*/nullptr,
         /*OwnsHeaderSearch =*/false);
+    if (!PreDefines.empty())
+      PP->setPredefines(PreDefines.str());
     PP->Initialize(*Target);
     PP->EnterMainSourceFile();
     return PP;
@@ -769,4 +772,46 @@ TEST(LexerPreambleTest, PreambleBounds) {
   }
 }
 
+TEST_F(LexerTest, CheckFirstPPToken) {
+  {
+    TrivialModuleLoader ModLoader;
+    auto PP = CreatePP("// This is a comment\n"
+                       "int a;",
+                       ModLoader);
+    Token Tok;
+    PP->Lex(Tok);
+    EXPECT_TRUE(Tok.is(tok::kw_int));
+    EXPECT_TRUE(PP->hasSeenMainFileFirstPPToken());
+    EXPECT_TRUE(PP->getMainFileFirstPPToken().isFirstPPToken());
+    EXPECT_TRUE(PP->getMainFileFirstPPToken().is(tok::kw_int));
+  }
+  {
+    TrivialModuleLoader ModLoader;
+    auto PP = CreatePP("// This is a comment\n"
+                       "#define FOO int\n"
+                       "FOO a;",
+                       ModLoader);
+    Token Tok;
+    PP->Lex(Tok);
+    EXPECT_TRUE(Tok.is(tok::kw_int));
+    EXPECT_TRUE(PP->hasSeenMainFileFirstPPToken());
+    EXPECT_TRUE(PP->getMainFileFirstPPToken().isFirstPPToken());
+    EXPECT_TRUE(PP->getMainFileFirstPPToken().is(tok::hash));
+  }
+
+  {
+    TrivialModuleLoader ModLoader;
+    auto PP = CreatePP("// This is a comment\n"
+                       "FOO a;",
+                       ModLoader, "#define FOO int\n");
+    Token Tok;
+    PP->Lex(Tok);
+    EXPECT_TRUE(Tok.is(tok::kw_int));
+    EXPECT_TRUE(PP->hasSeenMainFileFirstPPToken());
+    EXPECT_TRUE(PP->getMainFileFirstPPToken().isFirstPPToken());
+    EXPECT_TRUE(PP->getMainFileFirstPPToken().is(tok::identifier));
+    EXPECT_TRUE(
+        PP->getMainFileFirstPPToken().getIdentifierInfo()->isStr("FOO"));
+  }
+}
 } // anonymous namespace